This invention relates to ordnance devices which do not detonate thermally, such as bombs, warheads and rocket motors. In particular, this invention addresses the hazard created by such materials when exposed to accidentally caused external fires.
The transport and storage of ordnance devices frequently requires placing them in environments which have a high probability of open flames. Ordnance is frequently placed, for example, on the flight deck of an aircraft carrier where an aircraft fuel tank is also present. Accidental rupture of the fuel tank causes the spread of fuel over the flight deck, and the fire which results upon ignition of the spilled fuel can subject the rocket motors, warheads and other ordnance devices on the deck to dangerously high temperature and a high risk of ignition of the explosive material in the ordnance devices themselves. The rapid internal pressure buildup will result in case rupture and explosion with catastrophic results, including costly equipment losses and potential loss of life.
The present invention provides ordnance devices with the capability of limiting the response to non-propulsive vent burning when the ordnance device is subjected to externally applied heat. The localized weakening of the casing enclosing the explosive material results in the opening of a small vent hole of controlled size at a predetermined location on the casing to permit discharge of the explosive material and its combustion products without danger to the remainder of the casing and hence without the shattering of the casing and the uncontrolled propulsion of pieces of the casing in all directions.
The localized effect is achieved by affixing to the casing a solid mass containing two compositions --an ignition mix which upon ignition at a relatively low temperature reacts in a substantially non-gas-producing exothermic reaction, and a main reactant mix which ignites upon absorption of the energy released by the ignition mix, the main mix itself reacting exothermically to release sufficient thermal energy to degrade the casing. The two compositions may be comprised of granulated mixtures compressed into a pellet in the form of contiguous layers having a diameter equal to that of the area sought to be weakened. The pellet may then be secured to the casing interior with the ignition mix in direct contact with the interior surface of the casing. A number of such pellets may be strategically placed at various locations along the casing to provide maximal assurance that full venting of the explosion gases will occur without rupture of the casing other than at these locations.
Features which are desired in such a system and achieved by the present invention include:
1. Reaction products which possess sufficient residual thermal energy to degrade the metallic case strength;
2. Reactions which produce little or no gas which might deform or cause breakup of the grain of the surrounding propellant or explosive of the ordnance device itself and thereby raise the explosion hazard rather than lower it;
3. A configuration which permits ignition of the external surface of the ordnance propellant (or other explosive) in preferential locations with attendant case venting:
4. Self-initiation in a fuel fire and yet lack of response to the maximum aerodynamic heating to arise during missile flight;
5. A hazard no greater than that of the ordnance propellant or explosive, while using available materials of construction; and
6. Minimum thickness, taking up as little volume and weight of the total ordnance device as possible.
Further features and embodiments of the invention will be apparent from the following description.